Trying to stay healthy can seem like a full-time job sometimes.
Especially during a pandemic.
But I’m here to make that goal a little easier.
Welcome to the Nutrition Facts Podcast.
I’m your host Dr. Michael Greger.
Today, an acronym that needs a little explaining.
It’s called SIBO – S-I-B-O –
and it stands for Small Intestinal Bacterial Overgrowth.
Here’s my first story.
Gastrointestinal symptoms like abdominal pain
and bloating account for millions of doctor visits every year.
One of the conditions that may be considered for such a nonspecific
presentation of symptoms is SIBO: Small Intestinal Bacterial Overgrowth,
a concept that has gained popularity on the internet,
in addition to certain clinical and research circles.
SIBO is broadly defined as the excessive growth of
bacteria in the small intestine, and is typically treated with antibiotics.
But dispensing antibiotics to patients
with such nonspecifc, common symptoms is not without risks.
You could be fostering antibiotic resistance,
there could be side effects, and wiping out your good bacteria
could set you up for an invasion of bad bugs like C. diff,
all for a condition that may not even be real.
Even alternative medicine journals admit that SIBO
is being overdiagnosed, creating confusion and fear.
SIBO testing is overused and overly relied upon. Diagnoses are
often handed out quickly and without adequate substantiation.
Patients can be indoctrinated into thinking SIBO is a chronic condition
that cannot be cleared and will require lifelong management.
This is simply not true for most and is an example of the damage done
by overzealousness.
The monster that we now perceive SIBO to be may be no more than a phantom.
The traditional method for a diagnosis was a small bowel aspiration,
an invasive test where a long tube is snaked down your throat
to take a sample and count the bugs down there.
But this method has been almost entirely replaced with breath testing.
See, normally, a sugar called glucose is almost entirely absorbed
in the small intestine, so it never makes it down to the colon.
So if there is bacterial fermentation of that sugar, that suggests
you have bacteria up in your small intestine and can detect
that fermentation because the bacteria produce specific gases
that get absorbed in your blood stream and then are breathed out from
your lungs, which can then be detected with a breathalyzer-type machine.
Previously, a sugar called lactulose was used, but lactulose breath tests
weren't found to reliably detect the overgrowth of bacteria,
so researchers switched to glucose.
But when glucose was finally put to the test, it didn't work either.
The bacterial load in the small intestine was similar
for those testing positive or negative, so that's not a useful test either.
It turns out glucose can make it down to your colon after all.
They labeled the glucose dose with a tracer and found that almost half
of the positive results from glucose breath tests were false positives
because they were just fermenting it down in their colon
where your bacteria are supposed to be.
So patients incorrectly labeled with SIBO may undergo multiple courses
of antibiotics for a problem they don't even have.
Why do experts keep recommending breath testing then?
Oh, you mean the experts at the conference supported by
a breath testing company, most of whom had personally received funds
from SIBO testing or antibiotic companies?
And even if we could properly diagnose it, does it even matter?
In those with digestive symptoms, there is a range of positivity for SIBO
from approximately 4% to 84% —all over the map—
and there may be no difference in symptom scores between those testing
positive versus those testing negative, so testing positive could mean anything.
Who cares if some people have bacteria growing in their small intestines
if that doesn't necessarily correlate with symptoms?
Now antibiotics can make people with irritable bowel-type symptoms
diagnosed with SIBO feel better, so doesn't that prove SIBO was the cause?
No, because it can make just as many people feel better
who are negative for SIBO.
Currently rifaximin is most often used for SIBO, but it's not FDA-approved
for SIBO, so the cost can be prohibitive.
In fact, no drug has been approved for SIBO,
so even if you have good insurance, you may be shelling
out-of-pocket as much as $50 a day,
and you typically take it for two weeks.
And while antibiotics may help in the short-term,
they may make things worse in the long-term.
Those who are given a course of antibiotics are more than three times
as likely to report more bowel symptoms four months later than controls.
Finally today, it may not be the number of bacteria
growing in your small intestine, but the type of bacteria,
which can be corrected with diet.
If you test more than a thousand patients suffering from
irritable bowel-type symptoms such as excess gas, bloating,
diarrhea, abdominal pain for longer than six months,
who don't appear to have anything more serious going on, such as
inflammatory bowel disease, a significant percentage were found
to be suffering from lactose intolerance: intolerance to the milk sugar lactose.
In infancy we have an enzyme in our small intestines that
digests milk sugar, but most of us understandably lose it after weaning.
Although a genetic mutation has led to the persistence of the enzyme
in a minority of adults, about 75% of the world's population
malabsorb lactose and have lactose intolerance after age 30.
A third, though, were diagnosed with SIBO:
Small Intestinal Bacterial Overgrowth.
The evidence for SIBO and IBS symptoms is shrouded in controversy,
predominantly because of the fact that the breath tests used
in clinical practice to diagnose SIBO are not valid,
as I explored in the last video. And it's not even clear
what the implications are of having more versus less bacteria growing
in your small intestine since the number don't seem to correlate with symptoms.
It turns out it's not the number, but the type.
It's the kind of bugs you have growing in your small intestine.
So it's small intestinal microbial dysbiosis, not overgrowth in general,
but the wrong kind of growth that appears to underlie
symptoms associated with functional gastrointestinal disorders
like irritable bowel syndrome.
How can you prevent this from happening?
Well, the symptoms appeared be correlated to a significant drop
in the number of Prevotella species. Remember them?
Prevotella are healthy fiber feeders, suggestive of a higher fiber intake
in healthy individuals, while the bugs found more in symptomatic patients
ate sugar, which may reflect a higher dietary intake of sugars.
Yes, but correlation doesn't mean causation.
To prove cause and effect you have to put it to the test,
which is exactly what they did.
Switching a group of healthy individuals who habitually ate a higher fiber diet
to a more typical standard American low fiber diet with lots of sugar
produced striking results within just seven days.
First, 80% developed new gastrointestinal symptoms
out of the blue, such as bloating and abdominal pain that resolved
on resumption of their more healthful, habitual higher fiber diet. And the
diet related changes in the small intestinal microbiome were predictive
of symptoms and linked to an alteration in intestinal permeability;
in other words, they developed a leaky gut within seven days.
And while some went from SIBO positive to SIBO negative,
or SIBO negative to SIBO positive,
it didn't matter, since the number of bacteria growing
didn't correlate with symptoms. It was the type of bacteria growing.
And no wonder their guts got leaky. Short-chain fatty acid levels plummeted.
Those are the magical by-products that our good gut bugs make from fiber,
which play an important role in intestinal barrier integrity,
meaning keeping our gut from getting leaky. So while
we don't have sound data that something like a low FODMAP diet
has any benefit for SIBO-symptom patients,
there have been more than a dozen randomized controlled trials
putting fiber to the test, and overall there was a significant improvement
in symptoms among those randomized to increase their fiber intake.
That may actually help explain why high-fiber, plant-based diets
may prevent so many common diseases — the effect such diets have
on the composition and metabolic activity of our microbiome.
Our good gut bugs take the plant residues like fiber
and produce health-promoting and cancer-suppressing metabolites
like those short-chain fatty acids which have profound
anti-inflammatory properties.
All the evidence points to a physiological need
for about 50 grams of fiber a day,
which is the amount contained in the traditional African diet
and associated with the prevention of westernized diseases.
That's approximately twice what's typically recommended
and three times more than what most people are getting day-to-day.
Perhaps it should be no surprise we need so much.
Even though we split from chimpanzees millions of years ago,
there's still broad congruency in the composition
of our respective microbiomes to this day.
While they're still eating their 98-99% plant-based diets to feed their friendly
flora with fiber, we've largely removed fiber-rich foods from our food supply.
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